We have prepared two extracts from erythrocyte hemolysates obtained from spontaneously hypertensive rats which have a profound effect on blood pressure. One of the fractions produces a hypertensive elevation of the blood pressure in normatensive rats and stimulates calcium uptake by vascular tissue in vitro. The second fraction exerts a marked antihypertensive effect in spontaneously hypertensive rats, but has no detectable effect of the blood pressure of normotensive animals. In addition to the effect on blood pressure this fraction has an inhibitory effect on calcium uptake by aortic tissue in vitro. Both substances are associated with the cell membrane and appear to be relatively stable. The proposed study is to purify the two substances to homogeneity and perform preliminary biochemical characterizations. Calcium effects and blood pressure measurements will be used to determine the activity during the course of purification. Purification will be accomplished utilizing standard chromatographic techniques. The results obtained in this project will further our knowledge concerning hypertension and the regulation of blood pressure. It will established whether the compounds responsible for blood pressure alterations also influence calcium metabolism in vascular tissue. Future studies will attempt to determine the physiological properties and mechanisms of action of the substances.